Apparatus for transferring energy using onboard power electronics and method of manufacturing same

ABSTRACT

An apparatus comprises a first energy storage device configured to output a DC voltage, a first bi-directional voltage modification assembly coupled to the first energy storage device, and a charge bus coupled to the first energy storage device and to the first bi-directional voltage modification assembly. The apparatus also comprises high-impedance voltage source coupleable to the charge bus and a controller configured to monitor a transfer of charging energy supplied from the high-impedance voltage source to the first energy storage device. The controller is also configured to compare the monitored transfer of charging energy with a threshold value and, after the threshold value has been crossed, control the first bi-directional voltage modification assembly to modify one of a voltage and a current of the charging energy supplied to the first energy storage device.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to electric drive systemsincluding hybrid and electric vehicles and to stationary drives that aresubject to transient or pulsed loads and, more particularly, totransferring energy between an electrical storage device of the vehicleor drive and a power source external to the vehicle or drive.

Hybrid electric vehicles may combine an internal combustion engine andan electric motor powered by an energy storage device, such as atraction battery, to propel the vehicle. Such a combination may increaseoverall fuel efficiency by enabling the combustion engine and theelectric motor to each operate in respective ranges of increasedefficiency. Electric motors, for example, may be efficient ataccelerating from a standing start, while combustion engines may beefficient during sustained periods of constant engine operation, such asin highway driving. Having an electric motor to boost initialacceleration allows combustion engines in hybrid vehicles to be smallerand more fuel efficient.

Purely electric vehicles use stored electrical energy to power anelectric motor, which propels the vehicle and may also operate auxiliarydrives. Purely electric vehicles may use one or more sources of storedelectrical energy. For example, a first source of stored electricalenergy may be used to provide longer-lasting energy while a secondsource of stored electrical energy may be used to provide higher-powerenergy for, for example, acceleration.

Plug-in electric vehicles, whether of the hybrid electric type or of thepurely electric type, are configured to use electrical energy from anexternal source to recharge the traction battery. Such vehicles mayinclude on-road and off-road vehicles, golf cars, neighborhood electricvehicles, forklifts, and utility trucks as examples. These vehicles mayuse either off-board stationary battery chargers or on-board batterychargers to transfer electrical energy from a utility grid or renewableenergy source to the vehicle's on-board traction battery. Plug-invehicles may include circuitry and connections to facilitate therecharging of the traction battery from the utility grid or otherexternal source, for example. The battery charging circuitry, however,may include dedicated components such as boost converters,high-frequency filters, choppers, inductors, and other electricalcomponents dedicated only to transferring energy between the on-boardelectrical storage device and the external source. These additionaldedicated components add extra cost and weight to the vehicle.

It would therefore be desirable to provide an apparatus to facilitatethe transfer of electrical energy from an external source to theon-board electrical storage device of a plug-in vehicle that reduces thenumber of components dedicated only to transferring energy between theon-board electrical storage device and the external source.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an apparatus comprises a firstenergy storage device configured to output a DC voltage, a firstbi-directional voltage modification assembly coupled to the first energystorage device, and a charge bus coupled to the first energy storagedevice and to the first bi-directional voltage modification assembly.The apparatus also comprises high-impedance voltage source coupleable tothe charge bus and a controller configured to monitor a transfer ofcharging energy supplied from the high-impedance voltage source to thefirst energy storage device. The controller is also configured tocompare the monitored transfer of charging energy with a threshold valueand, after the threshold value has been crossed, control the firstbi-directional voltage modification assembly to modify one of a voltageand a current of the charging energy supplied to the first energystorage device.

In accordance with another aspect of the invention, a method comprisescoupling a battery to a first voltage bus, the battery configured tooutput a DC voltage, coupling a first bi-directional voltagemodification assembly to the first voltage bus and coupling a secondvoltage bus to the first voltage bus, the second voltage bus configuredto receive charging energy from a high-impedance voltage source and tosupply the charging energy to one of the first bi-directional voltagemodification assembly and the first voltage bus. The method alsocomprises configuring a controller to monitor a transfer of the chargingenergy to the battery, compare the monitored transfer of charging energywith a threshold value, and, after the threshold value has been crossed,control the first bi-directional voltage modification assembly to modifyone of a voltage and a current of the charging energy supplied to thebattery.

In accordance with yet another aspect of the invention, a systemcomprises a charge bus configured to receive charging energy from avoltage source, an energy storage device configured to output a DCvoltage and coupled to the charge bus, a first bi-directional voltagemodification assembly coupled to the charge bus and a controller. Thecontroller is configured to monitor a transfer of the charging energysupplied to the energy storage device, compare the monitored transfer ofcharging energy with a threshold comprising one of a voltage of theenergy storage device and an average rectified line voltage of thecharge bus, and, after the threshold has been crossed, control the firstbi-directional voltage modification assembly to modify one of a voltageand a current of the charging energy supplied to the first energystorage device.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a schematic diagram of a traction system according to anembodiment of the invention.

FIG. 2 is a schematic diagram of another traction system according to anembodiment of the invention.

FIG. 3 is a schematic diagram of another traction system according to anembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a traction system 10 according to anembodiment of the invention. Traction system 10 includes a first energystorage device 12. In one embodiment, first energy storage device 12 isa high-voltage energy storage device and may be a battery, a flywheelsystem, fuel cell, an ultracapacitor, or the like. First energy storagedevice 12 is coupled to a bi-directional voltage modification assembly14 via a DC bus 16. In one embodiment, bi-directional voltagemodification assembly 14 is a bi-directional DC-to-AC voltage inverter.Bi-directional DC-to-AC voltage inverter 14 includes six half phasemodules 18, 20, 22, 24, 26, and 28 that are paired to form three phases30, 32, and 34. Each phase 30, 32, 34 is coupled to a pair of conductors36, 38 of DC bus 16. An electromechanical device or motor 40 is coupledto bi-directional DC-to-AC voltage inverter 14. In one embodiment,electromechanical device 40 is a traction motor mechanically coupled toone or more driving wheels or axles 42 of a vehicle (not shown) or otherelectrical apparatus including cranes, elevators, or lifts.Electromechanical device 40 includes a plurality of windings 44, 46, and48 having a plurality of conductors 50 coupled to respective phases 30,32, 34 of bi-directional DC-to-AC voltage inverter 14. Windings 44-48also have a plurality of conductors 52 coupled together to form a node54.

Traction system 10 includes a controller 56 coupled to half phasemodules 18-28 via lines 58. Controller 56, through appropriate controlof half phase modules 18-28, is configured to control bi-directionalDC-to-AC voltage inverter 14 to convert a DC voltage or current on DCbus 16 to an AC voltage or current for supply to windings 44-48 viaconductors 50. Accordingly, the DC voltage or current from first energystorage device 12 may be converted into an AC voltage or current anddelivered to motor 40 to drive wheels 42. In other non-vehiclepropulsion systems, the drive wheels 42 may be another type of load (notshown), including a pump, fan, winch, crane, or other motor drivenloads. In a regenerative braking mode, electromechanical device 40 maybe operated as a generator to brake wheels 42 and to supply AC voltageor current to bi-directional DC-to-AC voltage inverter 14 for inversioninto a DC voltage or current onto DC bus 16 that is suitable forrecharging first energy storage device 12.

When a vehicle or apparatus incorporating traction system 10 is parkedor not in use, it may be desirable to plug the vehicle into, forexample, the utility grid or to a renewable energy source to refresh orrecharge energy storage device 12. Accordingly, FIG. 1 shows anembodiment of the invention including a charging system 60 coupled totraction system 10 for the recharging of energy storage device 12 suchthat components of traction system 10 may be used for the dual purposesof recharging energy storage device 12 and converting energy from energystorage devices 12 into energy usable to drive the load or propel thevehicle.

Charging system 60 includes an external, high-impedance voltage source62 having a plurality of conductors 64 coupled to a rectifier 66 andcoupled to a receptacle or plug 68 having contacts 70, 72. Whileexternal high-impedance voltage source 62 is shown as a poly-phaseutility system in FIGS. 1-3 having three phases, it is contemplated thatthe external, high-impedance poly-phase source could instead have one,two, six, or any other number of phases. Plug 68 is configured to matewith a plug 74 of traction system 10 having contacts 76, 78.High-impedance voltage source 62 includes secondary windings 80. Asshown in FIG. 3 hereinbelow, it is to be understood that source 62 wouldalso include primary windings not shown in FIG. 1 that are coupleable toa source such as the utility grid. Plug 74 is coupled to node 54, andeach winding 44-48 of motor 40 provides filtering for the chargingenergy supplied by high-impedance voltage source 62.

In a re-charging operation, charging energy, such as current, flows fromhigh-impedance voltage source 62 through rectifier 66, windings 44-48,and diodes 82, 84, 86 of respective half phase modules 18, 22, 26 tocharge bus 16 during a first stage of the re-charging operation. Thecharging energy from charge bus 16 flows into first energy storagedevice 12, which, in one embodiment, has an instantaneous acceptancecapability that is larger than an instantaneous delivery capability ofthe high-impedance voltage source 62. The charging energy is limited atleast by an impedance of high-impedance voltage source 62. Diodes 82-86are rated to allow current from the high impedance voltage source 62 toflow directly into first energy storage device 12 during the firststage. In this embodiment, diodes 88, 90, 92 of respective half phasemodules 20, 24, 28 are not configured to supply charging energy directlyfrom first energy storage device 12 to the charging bus 16. Accordingly,diodes 88-92 may have a lower current rating than diodes 82-86 and may,therefore, allow for reduced costs of traction system 10.

Returning to the re-charging operation, controller 56 is programmed orconfigured to monitor the charging energy supplied to first energystorage device 12 during the first stage. Since, in one embodiment,current of the charging energy during the first stage is greater thanthe current ratings of the components of bi-directional DC-to-AC voltageinverter 14 except for diodes 82-86, the charging energy flows onlythrough diodes 82-86 during the first stage. As the voltage rises infirst energy storage device 12, charging current tapers back. Controller56 is configured to monitor the current of the charging energy via acurrent sensor 94. While shown as sensing current flow between winding48 and diode 86, it is contemplated that current sensor 94 may be placedanywhere in traction system 10 such that current from the chargingenergy source may be sensed.

Controller 56 compares the monitored charging energy current to apre-determined threshold value. In one embodiment, the threshold valueis a value of the charging energy current that falls within a currentrating of all the components of bi-directional DC-to-AC voltage inverter14. The threshold value may also be based on a design and a temperatureof first energy storage device 12. Once controller 56 detects that thethreshold value has been crossed, controller 56 begins active control ofbi-directional DC-to-AC voltage inverter 14 during a second stage of there-charging operation. In this manner, re-charging of first energystorage device 12 during the first stage allows for rapid charging thatis limited primarily via the impedance of high-impedance voltage source62. During the second stage, charging is controlled due to thecomponents of bi-directional voltage modification assembly 14.

During the second stage, controller 56 controls half phase modules 18-28to boost the current and/or voltage of the charging energy suppliedthereto such that first energy storage device 12 may be re-charged to avoltage greater than that allowable through direct re-charging viahigh-impedance voltage source 62 without boosting. Respective pairs ofhalf phase modules 18-20, 22-24, 26-28 form individual boost convertersthat may operate at the same phase to reduce or eliminate high-frequencytorque ripple in motor 40. Furthermore, windings 44-48 act as boostinductors during the boosting operations.

Controller 56 senses a voltage of first energy storage device 12 via avoltage sensor 96 and regulates charging of first energy storage device12 such that its voltage does not exceed a specified level. Near the endof charging, controller 56 also regulates the re-charging voltage on DCbus 16 to a “float voltage” as the re-charging current tapers to lowlevels.

FIG. 2 shows a schematic diagram of a traction system 98 according toanother embodiment of the invention. Elements and components common totraction systems 10 and 98 will be discussed relative to the samereference numbers as appropriate. FIG. 3 will also discuss commoncomponents relative to the same reference numbers. In addition to thecomponents common with traction system 10, traction system 98 includes asecond energy storage device 100 coupled to DC bus 16 to provide powerto drive wheels 42. In one embodiment, second energy storage device 100is a low-voltage energy storage device and may be a battery, a fuelcell, an ultracapacitor, or the like. First energy storage device 12 maybe configured to provide a higher power than second energy storagedevice 100 to provide power during, for example, acceleration periods ofthe vehicle. Second energy storage device 100 may be configured toprovide a higher energy than first energy storage device 12 to provide alonger-lasting power to the vehicle to increase a travelling distancethereof.

A plurality of bi-directional DC-to-DC voltage converters 102, 104, 106are coupled to second energy storage device 100 and to DC bus 16 and areconfigured to convert one DC voltage into another DC voltage. Eachbi-directional DC-to-DC voltage converter 102-106 includes an inductor108 coupled to a pair of switches 110, 112 and coupled to a pair ofdiodes 114, 116. Each switch 110, 112 is coupled to a respective diode114, 116, and each switch/diode pair forms a respective half phasemodule 118, 120. Switches 110, 112 are shown, for illustrative purposes,as insulated gate bipolar transistors (IGBTs). However, embodiments ofthe invention are not limited to IGBTs. Any appropriate electronicswitch can be used, such as, for example, metal oxide semiconductorfield effect transistors (MOSFETs), bipolar junction transistors (BJTs),and metal oxide semiconductor controlled thyristors (MCTs).

Controller 56 is coupled to bi-directional DC-to-DC voltage converters102-106 via lines 58, and energy supplied via second energy storagedevice 100 is boosted by control of switches 110, 112 of bi-directionalDC-to-DC voltage converters 102-106 to supply the higher voltage to DCbus 16. The energy supplied via second energy storage device 100 to DCbus 16 is inverted via bi-directional DC-to-AC voltage inverter 14 andsupplied to motor electromechanical device 40. Similarly, energygenerated during a regenerative braking mode may also be used tore-charge second energy storage device 100 via bi-directional DC-to-ACvoltage inverter 14 and via bucking control of switches 110, 112 ofbi-directional DC-to-DC voltage converters 102-106.

As shown in FIG. 2, charging system 60 is coupled to DC/charge bus 16. Afirst switch or contactor 122 is coupled between second energy storagedevice 100 and charging bus 16. In a re-charging operation, controller56, which is coupled to switch 122, causes switch 122 to close, thusallowing charging energy from high-impedance voltage source 62 to flowdirectly into second energy storage device 100. In one embodiment,second energy storage device 100 has an instantaneous acceptancecapability that is larger than an instantaneous delivery capability ofthe high-impedance voltage source 62. During the first stage ofcharging, controller 56 monitors the charging voltage supplied to secondenergy storage device 100 via a voltage sensor 124.

Controller 56 compares the monitored charging voltage to apre-determined threshold value. In one embodiment, the threshold valueis a value of the voltage of second energy storage device 100. Thethreshold value may also be based on a design and a temperature ofsecond energy storage device 100. Since the instantaneous acceptancecapability of second energy storage device 100 is larger than theinstantaneous delivery capability of the high-impedance voltage source62, controller 56 monitors the voltage of second energy storage device100 such that its rated voltage is not exceeded. Accordingly, controller56 compares the monitored voltage of second energy storage device 100 toa voltage threshold value that has been pre-determined to be an optimalvalue to switch the re-charging operation to a second stage.

After the voltage threshold value has been crossed, controller 56 causesswitch 122 to open and begins active control of bi-directional DC-to-DCvoltage converters 102-106 to buck the voltage of the charging energysupplied thereto such that second energy storage device 100 may be moreslowly re-charged at a controlled and regulated pace to a desiredre-charge level. Controller 56 operates plurality of bi-directionalDC-to-DC voltage converters 102-106 such that a “float voltage” ofsecond energy storage device 100 may be maintained while current of thecharging energy flowing into second energy storage device 100 tapers tolow levels. A current sensor 126 allows controller 56 to set the currentof the charging energy to “top off” the energy stored in second energystorage device 100.

A switch or contactor 128 may also be coupled to conductor 36 tode-couple first energy storage device 12 from charge bus 16 during there-charging operation if desired. When the nominal voltage of the firstand second energy storage devices 12, 100 are appropriately selected andthe respective State of Charge (SOC) of each respective energy storagedevice 12, 100 is within predetermined values, switch 128 may also beclosed during the re-charging operation so that first energy storagedevice 12 may be simultaneously re-charged along with second energystorage device 100 as described below. Since charging energy is coupleddirectly to charge bus 16, bi-directional DC-to-AC voltage inverter 14is not used to boost the charging energy to re-charge first energystorage device 12 to a maximum level. A voltage sensor 130 coupled tocontroller 56 allows controller 56 to monitor the charging of firstenergy storage device 12.

In another embodiment, second energy storage device 100 may have aninstantaneous acceptance capability that is smaller than theinstantaneous delivery capability of the high-impedance voltage source62. Controller 56 may determine the instantaneous acceptance capabilityof second energy storage device 100, for example, by measuring its SOC.In this embodiment, controller 56 leaves switch 122 in its open stateand actively controls bi-directional DC-to-DC voltage converters 102-106to buck the voltage of the charging energy on charging bus 16 toregulate the voltage that is supplied to second energy storage device100 to a threshold or pre-determined value such that the desiredthreshold or re-charge level of second energy storage device 100 may becontrolled at a regulated pace. Control of bi-directional DC-to-DCvoltage converters 102-106 allows controller 56 to regulate the maximumcurrent applied to second energy storage device 100 to a desired ormaximum limit based on the design or parameters of second energy storagedevice 100.

When the desired threshold or re-charge level of second energy storagedevice 100 has been reached in the embodiments described herein,controller 56 may be programmed to terminate all stages of recharging.

FIG. 3 shows a schematic diagram of a traction system 132 according toanother embodiment of the invention. Elements and components common totraction systems 10, 98 and 132 will be discussed relative to the samereference numbers as appropriate. As shown, high-impedance voltagesource 62 includes a plurality of primary windings 134 coupled tosecondary windings 80. Primary windings 134 may be coupled to theutility grid. A plurality of inductors 136 is coupled to secondarywindings 80. It is to be understood that high-impedance voltage source62 as shown in FIG. 3 is applicable to the high-impedance voltagesources 62 shown in FIGS. 1 and 2.

High-impedance voltage source 62 is coupled to bi-directional DC-to-ACvoltage inverter 14. However, unlike that shown in FIG. 1, plug 74 iscoupled to bi-directional DC-to-AC voltage inverter 14 between diodes82-86 and windings 44-48. A plurality of switches or contactors 138 iscoupled to windings 44-48 such that, during a re-charging operation whencharging system 60 is coupled to traction system 132, motor 40 may bede-coupled therefrom so that the charging energy does not electricallyexcite or supply energy to motor 40 and therefore motor 40 does notcause the vehicle to move during charging.

In this embodiment, charging system 60 does not have a separaterectifier 66. Instead, diodes 82-92 provide the rectification to convertthe AC power supplied via high-impedance voltage source 62 to DC powerfor charge bus 16. In this embodiment, all diodes 82-92 are rated toallow current from the charging energy on charge bus 16 to flow directlyinto first or second energy storage devices 12, 100 during the firststage.

Similar to that described above with respect to FIG. 1, in a re-chargingoperation, charging energy flows from high-impedance voltage source 62through diodes 82-92 to charge bus 16 during a first stage of there-charging operation. The charging energy from charge bus 16 flows intofirst energy storage device 12 and into second energy storage device100, as described below. Controller 56 monitors and compares themonitored charging energy as described above to independently determinewhen to change the re-charging operation to the second stage for eachenergy storage device 12, 100. A plurality of inductors 140 (shown inphantom) may be included to assist the transformer leakage inductance,represented by windings 136, during the boosting operations if desired.It is contemplated that traction systems 10, 98 or FIGS. 1 and 2 mayalso include inductors 140 to assist transformer leakage inductanceduring the boosting operations if desired.

If contactor 122 is open and contactor 128 is closed, then energystorage device 12 is charged directly from high-impedance voltage source62 while energy storage device 100 is charged by bi-directionalconverters 102, 104, and 106 operating in buck mode, thus both energystorage device 12 and 100 can be charged simultaneously. If contactor128 is open and contactor 122 is closed, then energy storage device 100is charged directly from high-impedance voltage source 62 just asdescribed above in FIG. 2 during stage 1. When stage 2 is entered,contactor 122 opens, and stage 2 continues with the bi-directionalconverters 102, 104, and 106 controlling charge while operating in abuck mode. Energy storage device 12 could then be charged at a latertime either from high-impedance voltage source 62 with contactor 122open and contactor 128 closed or, if the high-impedance voltage source62 is unplugged from traction system 132, directly from energy storagedevice 100 (which typically has significantly more energy than energystorage device 12) through bidirectional converters 102, 104, and 106operating in boost mode. Bi-directional converters 102, 104, and 106 canbe operated with their switching phases shifted so as to reduce voltageand current ripple levels in both energy storage devices.

In another embodiment of the invention, during the charging of energystorage device 100 while in the second stage or mode of operation, with128 closed, controller 56 operates DC-AC inverter 14 to control orregulate voltage on DC charge bus 16 to a threshold value as sensedusing voltage sensor 130 using energy supplied by AC voltage source 62.Energy storage device 100 is capable of simultaneously being chargedthrough control of bidirectional converters 102, 104, and 106, or asubset thereof, operating in the buck mode.

Embodiments of the invention thus use components such as inverters,converters, filters and/or machine inductance already on-board atraction control system to recharge one or more energy storage devicesof the traction control system. In this manner, these components may beused for the dual purposes of motoring and recharging the energy storagedevices. Using the on-board components of the vehicles allows foroff-board charging stations to have a simple, low cost, high-powerdesign. In addition, a high-current charging may be obtained in a costeffective manner. Rapid, fast charging of the on-board energy storagedevices may be thus accomplished such that a large current flows intothe energy storage devices in a first re-charging stage that is mainlylimited by impedance of a voltage transformer without initial currentcontrol by electronic switching elements having higher current limitingproperties.

A technical contribution for the disclosed apparatus is that it providesfor a controller implemented technique for transferring energy usingonboard power electronics.

According to one embodiment of the invention, an apparatus comprises afirst energy storage device configured to output a DC voltage, a firstbi-directional voltage modification assembly coupled to the first energystorage device, and a charge bus coupled to the first energy storagedevice and to the first bi-directional voltage modification assembly.The apparatus also comprises high-impedance voltage source coupleable tothe charge bus and a controller configured to monitor a transfer ofcharging energy supplied from the high-impedance voltage source to thefirst energy storage device. The controller is also configured tocompare the monitored transfer of charging energy with a threshold valueand, after the threshold value has been crossed, control the firstbi-directional voltage modification assembly to modify one of a voltageand a current of the charging energy supplied to the first energystorage device.

In accordance with another embodiment of the invention, a methodcomprises coupling a battery to a first voltage bus, the batteryconfigured to output a DC voltage, coupling a first bi-directionalvoltage modification assembly to the first voltage bus and coupling asecond voltage bus to the first voltage bus, the second voltage busconfigured to receive charging energy from a high-impedance voltagesource and to supply the charging energy to one of the firstbi-directional voltage modification assembly and the first voltage bus.The method also comprises configuring a controller to monitor a transferof the charging energy to the battery, compare the monitored transfer ofcharging energy with a threshold value, and, after the threshold valuehas been crossed, control the first bi-directional voltage modificationassembly to modify one of a voltage and a current of the charging energysupplied to the battery.

In accordance with yet another embodiment of the invention, a systemcomprises a charge bus configured to receive charging energy from avoltage source, an energy storage device configured to output a DCvoltage and coupled to the charge bus, a first bi-directional voltagemodification assembly coupled to the charge bus and a controller. Thecontroller is configured to monitor a transfer of the charging energysupplied to the energy storage device, compare the monitored transfer ofcharging energy with a threshold comprising one of a voltage of theenergy storage device and an average rectified line voltage of thecharge bus, and, after the threshold has been crossed, control the firstbi-directional voltage modification assembly to modify one of a voltageand a current of the charging energy supplied to the first energystorage device.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. An apparatus comprising: a first energy storage device configured tooutput a DC voltage; a first bi-directional voltage modificationassembly coupled to the first energy storage device; a charge buscoupled to the first energy storage device and to the firstbi-directional voltage modification assembly; a high-impedance voltagesource coupleable to the charge bus; and a controller configured to:monitor a transfer of charging energy supplied from the high-impedancevoltage source to the first energy storage device; compare the monitoredtransfer of charging energy with a threshold value; and after thethreshold value has been crossed, control the first bi-directionalvoltage modification assembly to modify one of a voltage and a currentof the charging energy supplied to the first energy storage device. 2.The apparatus of claim 1 wherein the first energy storage devicecomprises a high power energy storage device having an instantaneousacceptance capability larger than an instantaneous delivery capabilityof the high-impedance voltage source; wherein the first bi-directionalvoltage modification assembly comprises a bi-directional DC-AC voltageinverter; and wherein the controller, in being configured to control thefirst bi-directional voltage modification assembly, is configured toboost one of the voltage and the current of the charging energy via thebi-directional DC-AC voltage inverter.
 3. The apparatus of claim 2wherein the high-impedance voltage source comprises: a plurality ofsecondary transformer windings; a rectifier bridge coupled to theplurality of secondary transformer windings.
 4. The apparatus of claim 2wherein the controller, in being configured to control the firstbi-directional voltage modification assembly, is configured to control aplurality of boost converters of the bi-directional DC-AC voltageinverter at a same phase.
 5. The apparatus of claim 2 wherein thebi-directional DC-AC voltage inverter comprises a plurality of diodesconfigured to transfer a current of the charging energy from thehigh-impedance voltage source to the charge bus before the thresholdvalue has been crossed.
 6. The apparatus of claim 2 wherein thecontroller, in being configured to compare the monitored transfer ofcharging energy with the threshold value, is configured to compare acurrent of the charge bus with a predetermined current threshold value.7. The apparatus of claim 1 wherein the first energy storage devicecomprises a low power energy storage device having an instantaneousacceptance capability larger than an instantaneous delivery capabilityof the high-impedance voltage source; wherein the first bi-directionalvoltage modification assembly comprises a bi-directional DC-DC voltageconverter; and wherein the controller, in being configured to controlthe first bi-directional voltage modification assembly, is configured tobuck one of the voltage and the current of the charging energy via thebi-directional DC-DC voltage converter.
 8. The apparatus of claim 7further comprising a switch having an open position and a closedposition; wherein the switch, when positioned in the closed position, isconfigured to couple the low power energy storage device directly to thecharge bus; wherein the switch, when positioned in the open position, isconfigured to de-couple the low power energy storage device directly tothe charge bus; and wherein the controller is further configured tocause the switch to change from the closed position to the open positionafter the threshold value has been crossed.
 9. The apparatus of claim 7further comprising a bi-directional DC-AC voltage inverter coupled tothe bi-directional DC-DC voltage converter and to the charge bus,wherein the bi-directional DC-AC voltage inverter is configured totransfer charging energy from the high-impedance voltage source to thecharge bus.
 10. The apparatus of claim 9 further comprising: a highpower energy storage device having an instantaneous acceptancecapability larger than an instantaneous delivery capability of thehigh-impedance voltage source; and wherein the controller is furtherconfigured to boost the voltage of the charging energy via thebi-directional DC-AC voltage inverter.
 11. The apparatus of claim 10wherein the controller is further programmed to simultaneously chargethe low power energy storage device and the high power energy storagedevice.
 12. The apparatus of claim 7 wherein the controller, in beingconfigured to compare the monitored transfer of charging energy with thethreshold value, is configured to compare a first energy storage devicevoltage of the charge bus with a predetermined voltage threshold value.13. The apparatus of claim 1 wherein the first energy storage devicecomprises a low power energy storage device having an instantaneousacceptance capability smaller than an instantaneous delivery capabilityof the high-impedance voltage source; wherein the first bi-directionalvoltage modification assembly comprises a bi-directional DC-DC voltageconverter; wherein the controller, in being configured to control thefirst bi-directional voltage modification assembly, is configured tobuck one of the voltage and the current of the charging energy via thebi-directional DC-DC voltage converter to a pre-determined value. 14.The apparatus of claim 1 wherein each of the first energy storage, thefirst bi-directional voltage modification, and the controller ispositioned on a vehicle.
 15. The apparatus of claim 1 wherein thehigh-impedance voltage source comprises one of a single-phasehigh-impedance voltage source, a two-phase high-impedance voltagesource, a three-phase high-impedance voltage source, and a six-phasehigh-impedance voltage source.
 16. A method for transferring energybetween an on-board electrical storage device and an external source,the method comprising: coupling a battery to a first voltage bus, thebattery configured to output a DC voltage; coupling a firstbi-directional voltage modification assembly to the first voltage bus;coupling a second voltage bus to the first voltage bus, the secondvoltage bus configured to receive charging energy from a high-impedancevoltage source and to supply the charging energy to one of the firstbi-directional voltage modification assembly and the first voltage bus;and configuring a controller to: monitor a transfer of the chargingenergy to the battery; compare the monitored transfer of charging energywith a threshold value; and after the threshold value has been crossed,control the first bi-directional voltage modification assembly to modifyone of a voltage and a current of the charging energy supplied to thebattery.
 17. The method of claim 16 wherein coupling the firstbi-directional voltage modification assembly to the first voltage buscomprises coupling a bi-directional DC-AC voltage inverter to the firstvoltage bus; and wherein configuring the controller to control the firstbi-directional voltage modification assembly comprises configuring thecontroller to boost a voltage of the charging energy via thebi-directional DC-AC voltage inverter.
 18. The method of claim 16wherein coupling the first bi-directional voltage modification assemblyto the first voltage bus comprises coupling a bi-directional DC-DCvoltage converter to the first voltage bus; and wherein configuring thecontroller to control the first bi-directional voltage modificationassembly comprises configuring the controller to buck a voltage of thecharging energy via the bi-directional DC-DC voltage converter.
 19. Themethod of claim 16 wherein configuring the controller to compare themonitored transfer of charging energy with the threshold value comprisesconfiguring the controller to one of: compare a current of the secondvoltage bus to a current threshold value; and compare a voltage of thebattery to a voltage threshold value.
 20. A system comprising: a chargebus configured to receive charging energy from a voltage source; anenergy storage device configured to output a DC voltage and coupled tothe charge bus; a first bi-directional voltage modification assemblycoupled to the charge bus; a controller configured to: monitor atransfer of the charging energy supplied to the energy storage device;compare the monitored transfer of charging energy with a thresholdcomprising one of a voltage of the energy storage device and an averagerectified line voltage of the charge bus; and after the threshold hasbeen crossed, control the first bi-directional voltage modificationassembly to modify one of a voltage and a current of the charging energysupplied to the first energy storage device.
 21. The system of claim 20wherein the voltage source comprises a high-impedance voltage source.22. The system of claim 20 wherein the first bi-directional voltagemodification assembly comprises a bi-directional DC-AC voltage inverter;and wherein the controller, in being configured to control the firstbi-directional voltage modification assembly, is configured to boost avoltage of the charging energy via the bi-directional DC-AC voltageinverter.
 23. The system of claim 20 wherein the first bi-directionalvoltage modification assembly comprises a bi-directional DC-DC voltageconverter; and wherein the controller, in being configured to controlthe first bi-directional voltage modification assembly, is configured tobuck a voltage of the charging energy via the bi-directional DC-DCvoltage converter.
 24. The system of claim 20 further comprising anelectrical apparatus configured to house the charge bus, the energystorage device, the first bi-directional voltage modification assembly,and the controller, wherein the electrical apparatus comprises one of avehicle, a crane, an elevator, and a lift.